Heat exchange method and apparatus

ABSTRACT

Cooling tubes of the type spaced along the cooling section of a continuous furnace are provided with means for changing the effective cooling length to control cooling of a workpiece passing through the cooling section.

1 51 May 15,1973

United States Patent 1191 Cope 6 6 XX M 6MN6 l/s 56 1.

8/1936 Petzold...................................

11/1914 Robinson FOREIGN PATENTS OR APPLICATIONS mm 3 uw 07 66 mm MW 0964 2634 3 1 9937 mmm 223 D N A O n m 0 o H m a M m E e G w N C y Hwm A Eww HAm w m [73] Assignee: The Electric Furnace Company,

Salem,0hio

' Jan. 29, 1971 271,382 3/1914 Germany...................,..........165/142 [22] Filed:

[2]] Appl. No.: 110,873 Primary ExaminerManuel A. Antonakas Attorney-Meyer, Tilberry and Body [57] ABSTRACT Cooling tubes of the type spaced along the cooling [58] Field of Search............................165/1,96, 142; section of a continuous furnace are provided with means for changing the effective cooling length to control cooling of a workpiece passing throu cooling section.

gh the 17 Claims, 8 Drawing Figures 3,622,299 Swillinger......'..Q.................,l65/96 X eLiL f PATENTH] HAY 1 51973 SHEET 1 0F 3 INVENTOR.

F. TROY (COPE Mew, Him 8 Bad;

FIG. I

ATTORNEYS PATENTED HAY I 51973 SHEET 2 BF 3 INVENTOR.

F. TROY COPE BY Mew, 711% Z 8044 PATENTEUHAY15|975 3.732.916

SHEET 3 [IF 3 FIG. 6

x DY STRIP WIDTH FIG.

STRIP TRAVEL XXXXXXXXXXX XXXXXXXXXXXXXX J x D I ,Y YXX O XX Q K MXXXXXXXXXXX XXXXI F TRO L ED JS 9% C BY Q v AFIGB M JMMQA,

ATTORNEYS 1 HEAT EXCHANGE METHOD AND APPARATUS BACKGROUND It is common practice to cool a continuously moving workpiece, such as a metal strip, by passing the strip through a cooling section or chamber provided with a plurality of transverse radiant cooling tubes on each side of the strip. These tubes consist of two nested conduits to direct a cooling medium, such as water, through the tube so that the tube forms a cooled radiant receiver for absorbing heat from the strip.

Strip which passes through such a cooling section often develops one or more hot bands over a substantial length of strip. Such hot bands result in finished strip which is not uniform, and which therefore has non-uniform physical characteristics 'which deviate signers. Such strip produces finished products which cannot pass inspection. The rejects must be scrapped,

and the costof producing such rejects is an undesirable burden on the manufacturing cost of the saleable end product.

Fortunately, testing techniques have been devised to detect such non-uniform characteristics in strip stock, and quality control techniques have also been developed to detect the presence of undesirable characteristics before the stock is shipped; more importantly, producers of strip must develop production techniques which eliminate such hot bands in the finished strip before it comes off the production line. This requires establishing procedures to eliminate hot (or cold bands before the strip has cooled enough to freeze the undesirable qualities in the strip stock i.e., before the I strip has passed a point beyond which the detect can be remedied.

SUMMARY OF THE INVENTION In accordance with the invention, a heat exchanger tube comprises two fluid conduits, one within the other and telescopically movable relative to each other, the inner tube defining one fluid flow path and the space between the tubes forming another fluid flow path. A baffle on the inner end of the inner conduit deflects fluid flow back toward the same end of the heat exchanger whence flow originates,'so that the effective heat exchange of the assembled tube is limited to that length in which the two conduits are coextensive. A plurality of such tubes spaced along the path of move ment of a metal strip in a strip mill form a treatment section in which cooling of the strip is controlled to achieve a uniform or nearly uniform temperature throughout any given transverse section of the strip. Such control is achieved by disposing some of the tubes so that the ends from which their heat exchange effectiveness begins are adjacent one edge of the strip, and disposing others so that the ends from which their effectiveness begins are adjacent the opposite edge ofthe strip, and then adjusting the heat exchangeefiective lengths of those tubes to eliminate hot bands that may form along a length of strip.

OBJECTS It is an object of the invention to provide heat exchange means for strip stock which produces a high degree of uniformity of temperature across the strip.

It is another object of the invention to cdol a moving strip of metal by means of heat exchangers extending 2 across the strip having a cooling capability across the entire strip but adjustable to limit the cooling capability to a length less than the entire strip width, some of such adjustable heat exchangers being effective beginning at one edge of the strip and others effective beginning at the other edge of the strip.

It is a further object of the invention to provide a heat exchanger tube having a fluid conduit within another fluid conduit and telescopic relative thereto, providing one fluid flow path within the inner conduit and a fluid flow path between'the conduits and means to move the conduits telescopically one relative to the other.

It is still another object of the invention to provide a heat exchanger tubecom'prising two fluid conduits one within the other and having telescopic relative movement, the inner conduit provided. with means to turn the fluid flow whereby to confine fluid flow in the two opposite directions to the portion of the two conduits coextensive with each other.

a and arrangements of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof and wherein:

FIG. 1' is a top planIview with parts broken away and in section, being a view in section substantially on line 1-1 of FIG. 2;, showingapreferred embodiment of the invention;

FIG. 2- is a side elevational view substantially from the position of line 2-2 of FIG. 1, and with parts broken away to show details;

FIG. 3 is a view ii -section through a heat exchange tube made in accordance with one embodiment of the invention; i n

FIG. 4 is a cross-sectional elevational view looking in the direction of arrows 4 4 in FIG. 3;

FIG. 5 is a cross-sectional, elevational view looking in i the direction. of arrows 5-5 in FIG. 3;

FIG. 6 is a graph which shows a temperature gradient across the metal strip being heat treated and having a hot band between its edges which a heat treat section made according to this invention is designed to remedy;

FIG. 7 is another temperature gradient curve showing a possible temperature gradient from bottom to top of the strip and illustrating an inequality in the strip temperature, which inequality is correctible in a heat treat section made according to this invention; and

FIG. 8 is a schematic view along; the general lines of FIG. 1 but presenting a schematic showing of the heat exchange tubes and the metal strip which is being heat treated, along with appropriate shading of the tubes to illustrate the practice of the method aspects of the invention.

DESCRIPTION OF E PREFERRED EMBODIMENTS Referring now to the drawings, wherein the illustrations are for purposes of showing the preferred embodi- C, are rotatably carried by walls A and B to support a metal strip D having edges L and R. Strip D moves longitudinally through the heat treat chamber on rollers C.

,'.with tubes E and with their telescope ends F arranged adjacent to left edge L of strip D. Other heat exchange 7 tubes 6,, and G are spaced along the path of movement of strip D, supported in and by walls A and B, above strip D. Tubes G and G alternate with each other, with the telescope ends F of tubes 6,, being adjacent left edge L of strip D, and telescope ends F of tubesG being adjacent right edge R of strip D.

Heat exchange tubes E E G and G are adapted to be supplied with a heat exchange medium, and manifolds H and l are shown connected for that purpose, the manifolds I being indicated schematically in dotted-line form.

In accordance with a preferred arrangement, each heat exchange tube E E G and G comprises two telescoping conduits, an outer conduit 2 and an inner conduit 4. Each outer conduit 2 extends through one of brick walls A or B and has one end received in a recess 6 in the opposite brick wall. Thus, outer conduits 2 of tubes E and G pass through suitable openings in brick wall B and are secured thereto by flange assemblies 7, while the left ends thereof, as seen in FIG. 1, are secured in brick wall A by means of recesses 6. The right end portions of tubes E and G have outer conduits 2 thereof connected with manifolds H as by connections 14 at telescope ends F of the tubes. Telescope ends F are furthermore provided with suitable openings, as at in FIG. 3, through which conduits 4 slidably pass to provide the telescopic relation between conduits 2 and 4 referred to above.

Each conduit 4 has an inner end which is disposed inside outer conduit 2, and another end which is disposed outside conduit 2. The inner ends of the inner conduits may be provided with deflectors 8 as shown in FIG. 3. Deflector 8 is secured to the inner end of conduit 4 in outwardly spaced relationship thereto by three circumferentially spaced rods 9 welded to deflector 8 and conduit 4. At least one of rods 9 may be longer than the others to extend beyond deflector 8 and serve as a stop by striking closed end 10 of conduit 2 in the maximum telescoped position of conduit 4. In the maximum telescoped position, deflector 8 is substantially aligned with the inner surface of wall A so that coolant is not circulated in that portion of conduit 2 positioned in recess 6. This arrangement prevents heat loss from wall A. Deflector 8 is of smaller diameter than the inner diameter of conduit 2. In one arrangement, deflector 8 has a diameter around one-fourth inch less than the inner diameter of conduit 2. Deflector 8 is preferably dished and has its concave surface facing the open inner end of conduit 4.

In accordance with one arrangement, conduit 4 has four circumferentially spaced radially extending pro jections l2 welded to the outer surface thereof for slidably maintaining conduit 4 centrally located within conduit 2. Four such projections may be provided at longitudinally spaced locations along conduit 4. One or more openings 12 may be provided on the inner conduit 4 immediately adjacent the point of attachment to the deflector 8 and along its length.

Closely adjacent its telescope end F, each outer conduit 2 is provided with a fluid connection 14 which communicates with the manifold H. Because each inner conduit 4 is adapted for telescopic movement relative to outer conduit 2, the outer end of each conduit 4 is preferably connected by a suitable flexible connection such as a rubber or the like hose with the manifold I, the manifold I and its connection with conduits 4 being shown schematically as indicated above. Manifolds H are connected with the inlet of a fan so that coolant fluid flows into conduits 4 from manifolds I, out of the open inner ends of conduits 4, axially along the space between conduits 2 and 4, through connections 14 and into manifolds l-I. Conduits 4 are of substantially smaller diameter than conduits 2 so that a radial space is provided between the inner periphery of conduits 2 and the outer periphery of conduits 4. In the preferred arrangement, the cross-sectional area of this radial space is at least as great as the cross-sectional area of the inner periphery of conduit 4.

Passing now to a consideration of FIGS. 6, 7 and 8, it will be noted that a condition may develop in the heat treatment of a metal strip wherein a band of metal between the edges becomes considerably hotter than the remainder of the strip. Such a condition is illustrated in the temperature curve in FIG. 6, wherein a band between D and Dy is shown as having a higher temperature T, than the rest of the strip. Such a condition is correctible in a heat treat section made according to this invention, as will be evident from a more detailed consideration of the schematic view shown in FIG. 8. For the purposes of this discussion, it will be assumed that the temperature across the strip remains substantially uniform as the strip moves downward in FIG. 8 until the strip reaches the break-line K-K in this fig ure. Accordingly, it may be assumed that the heat exchange tubes down to the break-line K-K are used in such a manner that the heat exchange capability of each tube above break-line K-K is the maximum ca pacity for each tube, shown by the double crosshatching from L to R. In other words, each tube above the break-line K-K is assumed to be disposed with the inner end of the inner conduit as close to the closed end of the outer conduit as it can be placed.

At or in the vicinity of the break-line K--K, the hot band D to Dy has been detected and an effort is to be made to correct the hot band in the strip. Assuming that the first heat exchange tube below the break-line is effective from the right edge R of strip D, then the second tube removed from break-line K-K will be oriented to be effective from the left edge L of strip D and the remaining tubes will alternate in that manner. .Accordingly, the first tube below break-line K-K will be arranged so that its heat exchange effectiveness extends from a point D to the right edge of strip D. The next tube is arranged so that its heat exchange effectiveness extends from a point Dy to the left edge of the strip D. Thus, the effective heat exchange length of the first tube below the break-line K-K is shown by double cross-hatching as T and the effective heat exchange length of the second tube below the break-line is shown as T It will be noted that the two effective heat exchange lengths T, and T overlap at the hot band extending from D to Dy. Such overlapping is shown as carrying through in the next two heat exchange tubes so that the third tube is effective over a length T which is shown as substantially the same as the heat exchange length of the first tube below the break-line, and the next tube down is shown as having a heat exchange effective length of T and so forth. Thus, the overlap of the heat exchange lengths of the first four tubes extends from the left edge D of the hot band to the right edge Dy of the hot band. This overlap of-heat exchange effective lengths iscontinued as long as'necessary to eliminate the hot band in the strip of metal being cooled in this particular heat treat section of the operation.

It will moreover be apparent from a consideration of the drawings in detail, especially FIGS. 3,4 and 5 that the heat exchange length is varied or shortened from the maximum capability of the tube by pulling the inner conduit out of the outer conduit to some extent so as to pull the open, inner end of the 'inner conduit away from the closed end of the outer conduit. For example, referring to FIG. 3, as the inner end of inner conduit 4 is moved rightward as seen in this figure, the dead-end space to the left of the inner end of the inner conduit and deflector 8 increases, and the effective heat exchange length of the tube diminishes to some length less than the full length of the tube across the entire width of strip D. It will be noted that the heat exchange capability which remains is effective from the right edge of strip D. correspondingly, the heat exchange tubes next adjacent the one shown in FIG. 3 will be effective as heat exchangers from left edge L of strip D.

If now a condition be assumed in which two bands along the edge of stripD are hotter than a handsomewhere between the left and rightedges, then the heat exchange chamber here disclosed can be adjusted as reflected diagrammatically by the two effective heat exchange lengths shown near the bottom of FIG. 8, namely T, and T The two heat exchange tubes there shown are arranged with their heat exchange effective lengths less than enough to overlap by a band width shown as D Only two such heat exchange tubes are shown in FIG. 8, namely T and T but it will be understood by those skilled in the art that additional heat exchange tubes may be thus arranged for as long an interval of travel of strip D as may be required to correct the condition noted.

If the condition indicated in FIG. 7 be now considered, it will be noted that the curve there shown indicates that strip D is hotter at its upper surface than at its lower surface. Such a condition is correctible by a number of approaches in a heat exchange section made according to this invention. First, one or more of the heat exchange tube in the lower row, namely tubes E and E may be closed completely to bring the temperature of the bottom of the strip up to the temperature 'at the top. Alternatively, the heat exchange tubes E and E again those disposed below the hot strip, can be arranged so that their heat exchange effectiveness extends across only half of the strip width. In such a case, a predetermined number of tubes E would be arranged so that their heat exchange effectiveness would be half of the strip D, and a like number of tubes E would similarly be arranged to be effective over half of their length. The tubes E would be effective to cool the right half of the strip, while the tubes E would be effective to cool the left half of the strip. The total cooling effect of the number of tubes E and E thus involved would be half of their total effectiveness as if they were operating at full capacity.

In the arrangement shown and described, tubes E and E; are positioned below strip D while tubes 6,, and G are positioned above strip D. Tubes E and E, are reversely positioned relative to one another so that telescope ends F of tubes E are located adjacent wall A, while telescope ends F of tubes E are located adjacent wall B. Tubes 6,, and G; are also reversely positioned so that telescope ends F of tubes 6,, are located adjacent wall A, while telescope ends F of tubes 6,; are located adjacent wall B. This reverse positioning arrangement alternates throughout the length of the heat exchange chamber.

It will be recognized that either a liquid or a gas may be circulated through tubes E E G and G The circulating fluid may be heated or cooled by a heat exchanger so that heat is radiated from strip D to the tubes; or is radiated from the tubes to strip D. Thus, the present arrangement maintains a uniform temperature transversely of strip D whether strip D is being heated or cooled. The flow of fluid through conduits 2 and 4 may also be reversed from the direction indicated in the drawing.

It will berecognized that the tubes define heat exchange means and the telescopic arrangement of the inner and outer conduits defines a selective adjustment means for. selectively varying the effective length of the heat transfer means. The telescopic adjustment also varies the spacing between the open inner end of inner conduit 4, and the connection between outer conduit 2 and manifold H. The arrangement of the present invention varies the heat exchange rate between strip D and the tubes independently of the temperature of the heat exchange fluid and the rate of fluid circulation.

Depending upon the direction in which heat exchange fluid is circulated, one of conduits 2 or 4' will have afluid inlet opening, while the other will have a fluid outlet opening. The telescopic adjustment varies the longitudinal spacing between the inlet and outlet to vary the effective heat exchange length. When the effective length of a tube is changed, the heat exchange rate of the entire tube is changed independently of changing the temperature of the heat exchange fluid or its rate of flow.

While the invention has been described with reference to a preferred embodiment, obvious modifications and alterations will occur to others upon reading and understanding this specification. It isintended that all such. modifications and alterations be included insofar as they come within the scope of the appended claims or the equivalence thereof. V

Having thus described my invention, I claim:

1. An elongated hollow heat exchange means for exchanging heat, fluid inlet and outlet opening means in said heat exchange means for circulating heat exchange fluid through said heat exchange means, selective adjustment means for varying the length of said heat exchange means through which heat exchange fluid is circulated in passing between said inlet and outlet opening means, said adjustment means being operative between a maximum heat exchange position wherein heat exchange fluid is circulated through substantially the entire length of said heat exchange means and intermediate heat exchange positions wherein heat exchange fluid is circulated through less than the entire length of said heat exchange means, whereby the length of said heat exchange means which is effective to transfer heat is varied by varying the total length of said heatexchange means through which heat exchange fluid is circulated.

2. The device of claim 1 wherein said heat exchange means includes inner and outer elongated hollow conduits, said inlet opening means being in one of said conduits and said outlet opening means being in the other of said conduits, and at least one of said conduits being axially movable relative to the other of said conduits to define said selective adjustment means.

3. The device of claim 2 wherein said inner conduit has an inner end portion positioned within said outer conduit and one of said opening means is in said inner end portion of said inner conduit, said outer conduit having opposite end portions and the other of said opening means being in one of said end portions of said outer conduit, whereby axial movement of said one conduit relative to said other conduit varies the axial spacing between said inlet and outlet opening means.

4. The device of claim 3 and further including fluid deflector means positioned on said inner end of said inner conduit.

5. The device of claim 1 wherein said heat exchange means includes a first fluid conduit having a closed first end and having one of said fluid opening means at its other end, a second fluid conduit positioned within said first conduit, said second conduit having a first end positioned within said first conduit and a second end positioned outside of said first conduit, the other of said fluid opening means being in said first end ofsaid second conduit, fluid connection means on said second end of said second conduit, said adjustment means varying the distance between said fluid inlet and outlet opening means axially of said conduits.

6. The device of claim 5 wherein said adjustment means includes means for moving at least one of said conduits axially relative to the other of said conduits.

7. The device of claim 6 and further including fluid deflector means positioned at said first end of said second conduit for deflecting fluid flowing through said fluid inlet opening means to said fluid outlet opening means.

8. The device of claim 1 and further including a heat exchange apparatus for heat treating material moving through said apparatus, said apparatus having a plurality of said heat exchange means positioned therein.

9. The device of claim 8 wherein material moves through said apparatus in a predetermined direction and said plurality of said heat exchange means are positioned in spaced-apart relationship in said predetermined direction and extend transversely of said predetermined direction.

10. The device of claim 9 wherein at least certain of said plurality of heat exchange means are reversely positioned relative to adjacent ones of said plurality of said heat exchange means.

11. The device of claim 9 wherein at least certain of said plurality of heat exchange means include inner and outer elongated hollow conduits, one of said conduits having said inlet opening means therein and the other of said conduits having said outlet opening means therein, at least one of said conduits of said certain heat exchange means being axially movable relative to the other of said conduits to vary the axial spacing between said inlet and outlet opening means to define said adjustment means.

12. The device of claim 11 wherein said inner conduit of said certain heat exchange means has an inner end portion positioned within said outer conduit and one of said fluid opening means is in said inner end portion of said inner conduit, said outer conduit having opposite end portions and the other of said fluid opening means being in one of said end portions of said outer conduit.

13. The device of claim 12 wherein said certain heat exchange means are reversely positioned in said apparatus so that some of said certain heat exchange means have said one end portions thereof positioned on one side of said apparatus and other of said certain heat exchange means have said one end portions thereof positioned on the other side of said apparatus.

14. A heat treating apparatus through which strip material passes in a longitudinal direction, a plurality of elongated hollow heat exchange means spaced-apart in said longitudinal direction and extending transversely of said longitudinal direction, fluid inlet and outlet opening means in said heat exchange means for circulating heat exchange fluid through said heat exchange means, and selective adjustment means on at least certain of said heat exchange means for selectively varying the length of said heat exchange means through which heat exchange fluid is circulated to control the temperature gradient across the width of strip material passing through said apparatus, said adjustment means being operative between a maximum heat exchange position wherein heat exchange fluid is circulated through substantially the entire length of said heat exchange means and intermediate heat exchange positions wherein heat exchange fluid is circulated through less than the entire length of said heat exchange means, whereby the length of said heat exchange means which is effective to transfer heat is varied by varying the total length of said heat exchange means through which heat exchange fluid is circulated.

15. A method of heat treating material comprising the steps of; passing material through a heat exchange apparatus, circulating heat exchange fluid through elongated hollow conduit heat exchange means in said apparatus for exchanging heat between said fluid and said material, and selectively varying the length of said heat exchange means through which heat exchange fluid is circulated for varying the length of said heat exchange means which is effective to transfer heat.

16. The method of claim 15 wherein said elongated hollow conduit means includes inner and outer tubes and the effective length of said conduit means is varied by axially moving at least one of said tubes relative to the other.

17. The method of claim 15 wherein said apparatus is for heat treating strip material having a predetermined width and movable through said apparatus in a longitudinal direction, said heat exchange means in.- cluding a plurality of conduit means extending transversely of the direction of movement of strip material through said apparatus, said step of varying the heat exchange rate of said heat exchange means being per formed by limiting the flow of circulating heat exchange fluid in at least certain of said conduit means over a length less than the width of strip material passing through said apparatus. 

1. An elongated hollow heat exchange means for exchanging heat, fluid inlet and outlet opening means in said heat exchange means for circulating heat exchange fluid through said heat exchange means, selective adjustment means for varying the length of said heat exchange means through which heat exchange fluid is circulated in passing between said inlet and outlet opening means, said adjustment means being operative between a maximum heat exchange position wherein heat exchange fluid is circulated through substantially the entire length of said heat exchange means and intermediate heat exchange positions wherein heat exchange fluid is circulated through less than the entire length of said heat exchange means, whereby the length of said heat exchange means which is effective to transfer heat is varied by varying the total length of said heat exchange means through which heat exchange fluid is circulated.
 2. The device of claim 1 wherein said heat exchange means includes inner and outer elongated hollow conduits, said inlet opening means being in one of said conduits and said outlet opening means being in the other of said conduits, and at least one of said conduits being axially movable relative to the other of said conduits to define said selective adjustment means.
 3. The device of claim 2 wherein said inner conduit has an inner end portion positioned within said outer conduit and one of said opening means is in said inner end portion of said inner conduit, said outer conduit having opposite end portions and the other of said opening means being in one of said end portions of said outer conduit, whereby axial movement of said one conduit relative to said other conduit varies the axial spacing between said inlet and outlet opening means.
 4. The device of claim 3 and further including fluid deflector means positioned on said inner end of said inner conduit.
 5. The device of claim 1 wherein said heat exchange means includes a first fluid conduit having a closed first end and having one of said fluid opening means at its other end, a second fluid conduit positioned within said first conduit, said second conduit having a first end positioned within said first conduit and a second end positioned outside of said first conduit, the other of said fluid opening means being in said first end of said second conduit, fluid connection means on said second end of said second conduit, said adjustment means varying the distance between said fluid inlet and outlet opening means axially of said conduits.
 6. The device of claim 5 wherein said adjustment means includes means for moving at least one of said conduits axially relative to the other of said conduits.
 7. The device of claim 6 and further including fluid deflector means positioned at said first end of Said second conduit for deflecting fluid flowing through said fluid inlet opening means to said fluid outlet opening means.
 8. The device of claim 1 and further including a heat exchange apparatus for heat treating material moving through said apparatus, said apparatus having a plurality of said heat exchange means positioned therein.
 9. The device of claim 8 wherein material moves through said apparatus in a predetermined direction and said plurality of said heat exchange means are positioned in spaced-apart relationship in said predetermined direction and extend transversely of said predetermined direction.
 10. The device of claim 9 wherein at least certain of said plurality of heat exchange means are reversely positioned relative to adjacent ones of said plurality of said heat exchange means.
 11. The device of claim 9 wherein at least certain of said plurality of heat exchange means include inner and outer elongated hollow conduits, one of said conduits having said inlet opening means therein and the other of said conduits having said outlet opening means therein, at least one of said conduits of said certain heat exchange means being axially movable relative to the other of said conduits to vary the axial spacing between said inlet and outlet opening means to define said adjustment means.
 12. The device of claim 11 wherein said inner conduit of said certain heat exchange means has an inner end portion positioned within said outer conduit and one of said fluid opening means is in said inner end portion of said inner conduit, said outer conduit having opposite end portions and the other of said fluid opening means being in one of said end portions of said outer conduit.
 13. The device of claim 12 wherein said certain heat exchange means are reversely positioned in said apparatus so that some of said certain heat exchange means have said one end portions thereof positioned on one side of said apparatus and other of said certain heat exchange means have said one end portions thereof positioned on the other side of said apparatus.
 14. A heat treating apparatus through which strip material passes in a longitudinal direction, a plurality of elongated hollow heat exchange means spaced-apart in said longitudinal direction and extending transversely of said longitudinal direction, fluid inlet and outlet opening means in said heat exchange means for circulating heat exchange fluid through said heat exchange means, and selective adjustment means on at least certain of said heat exchange means for selectively varying the length of said heat exchange means through which heat exchange fluid is circulated to control the temperature gradient across the width of strip material passing through said apparatus, said adjustment means being operative between a maximum heat exchange position wherein heat exchange fluid is circulated through substantially the entire length of said heat exchange means and intermediate heat exchange positions wherein heat exchange fluid is circulated through less than the entire length of said heat exchange means, whereby the length of said heat exchange means which is effective to transfer heat is varied by varying the total length of said heat exchange means through which heat exchange fluid is circulated.
 15. A method of heat treating material comprising the steps of; passing material through a heat exchange apparatus, circulating heat exchange fluid through elongated hollow conduit heat exchange means in said apparatus for exchanging heat between said fluid and said material, and selectively varying the length of said heat exchange means through which heat exchange fluid is circulated for varying the length of said heat exchange means which is effective to transfer heat.
 16. The method of claim 15 wherein said elongated hollow conduit means includes inner and outer tubes and the effective length of said conduit means is varied by axially moving at least one of said tubes relative to the other.
 17. The method of claim 15 wherein said appaRatus is for heat treating strip material having a predetermined width and movable through said apparatus in a longitudinal direction, said heat exchange means including a plurality of conduit means extending transversely of the direction of movement of strip material through said apparatus, said step of varying the heat exchange rate of said heat exchange means being performed by limiting the flow of circulating heat exchange fluid in at least certain of said conduit means over a length less than the width of strip material passing through said apparatus. 